Electrode support for electron discharge devices



July'l9, A1960 ELECTRODE SUPPORT FOR ELECTRON- DISCHARGE DEVICES FiledMay 5, 1959 v l.INVENTORS HERBERT H. CHUN YLOUIS W. ROBERTS ATTORNEY H;.al CHUIQ ,mL 2,945,983

2 Sheets-Sheet 1 July 19, 1960 H. H. cHuN :TAL K ELECTRODE SUPPORT FORELECTRON DISCHARGE DEVICES. Filed may s, 1959 2 sheets-sheet 2 I...sflabf 3 l 2 n L 69 7 32 3 e O a e m l L. 55 i 2 l 2 ,f 17H Bp,//f//f/ 3 L l l .l a s\ l .h w 33 7- ...nh vT 3 FIG. 2

INVENTORS 'HERBERT H. CHUN BY LOUIS w. ROBERTS ATTORNEY ELECTRUDESUPPORT FOR ELECTRON DISCHARGE DEVICES Filed May 5, 1959, Ser. No.811,121

Claims. (Cl S15-39.3)

The present invention relates generally to electron discharge devices ofthe backward wave oscillator and/or amplier type and more particularlyto an improved electrode structure for such devices.

Backward wave tubes of the Carcinotron -type generally comprise spacedparallel conductors `defining therebetween an interaction space. Anelectron beam emitted by a suitable gun source traverses the interactionspace and is influenced by a crossed electric and magnetic iieldestablished between the conductors. A delay line comprising interdigitalmetallic fingers forms one of the boundaries of the interaction spacewhile the sole electrode forms the other boundary. Biasing voltagedifferentials provided by the parallel conductors as well as a grid andaccelerator electrode control the electron beam configuration and thetube operation.

Generally it is considered that the sole electrode must be perfectlysymmetrical with respect to an interdigital delay line for optimum tubeperformance. For various reasons, however, it has been observed thatlthe symmetrical position may not `be the most desirable electricallyfrom tube to tube. In the normal steady state operation of backward waveoscillator tubes, it is assumed that a balance of the electric andmagnetic forces exists at every .point in the electron beam and that thebeam current ilow. is rectilinear. It is noted, however, that theelectric field between the sole electrode and the anode varies becauseof the charge on the beam. It therefore, follows that it is impossibleto predetermine the critical placement of the sole electrode withrespect to the delay line circuit due to a lack of control of the chargedis-V tribution in the beam at any arbitrary point in its path.

Itis an object of the present invention to provide means to externallyoptimize electrical performance of a backward wave oscillator and/oramplifier tube.

A further object of the invention is to provide an improved electrodestructure for a backward wave oscillator and/ or amplifier tube tofacilitate external adjustment of the electrode after completion of tubefabrication. v

A still further object is lto provide an improved sole electrode supportfor a backward wave oscillator and/or amplifier tube which may bereadily adjusted after completion of fabrication to increase efficiencyand power output.

The embodiment of the invention will be described with reference to abackward wave structure of circular conguration found in a CarcinotronIt may be presumed that perfectly concentric spacing will produceoptimum electrical characteristics. With experience gained inmanufacturing, however, it has been noted that beam currentcharacteristics may vary from tube to tube. In accordance with theteachings of the invention we provide an adjust- States Patent() lCe ingmechanism coupled directly to the sole electrode by means of anon-magnetic metal member attached thereto. The sole electrode may bemoved axially and also radially by a simple manipulation of theadjusting mechanism which may be achieved externally after the tube has'been completely fabricated and evacuated. It is a feature of theinvention that the tube may be operated and then adjusted foroptimum'performance electrically.

The advantages of the invention include increased efficiency over aselected frequency band as compared to pre-positioned prior artelectrode structures as well as increased power outputs of from 20% to100% over the band as compared with tubes not incorporating theadjustable electrode structure. Furthermore, holes and power dips haveAbeen considerably reduced across the frequency band and a tube havingimproved resistance to vibration and shock has resulted from the novelstructure for mounting of the sole electrode.

Additional objects, features and advantages will be apparent afterconsideration of the following detailed description and -theaccompanying drawings, in which:

Fig. l is a perspective view of the illustrative embodiment with aportion of the magnet structure broken laway to reveal the internalstructure; y

Fig. 2 is a detailed cross-sectional view along theline 2 2 in Fig. 1with the magnets omitted, and

Fig. 3 is a detailed plan view along the line 3-3 in Fig. 2. Y I

Referring to Fig. l the embodiment of the invention 1 comprises acircular metallic body member 2 enclosed by topand bottom` cover plates3 and 4 tovthereby define a vacuum tight envelope. Before proceeding toa descrip'- tion of the structure within the envelope it may be notedthat oppositely disposed toroidal magnets 5 and 6 surround the envelopeto provide the magnetic eld for operation of the tube.

Spaced within the envelope is a `circular' metallic conductor comprisingan interdigital delay line 7 having opposed iingers 8 and '9. extendingfrom ring member 10 and 11. The delay line assembly is secu-relypositioned by means of a shoulder or step 12 and l'in body member 2',Concentrically disposed within the delay line structure is the soleelectrode 14 which is supported by the improved adjust-ing mechanism ofthe invention now to be described.

The sole electrode 1.4 fabricated of a highly conductive oxygen-freemetal such as copper forms together with the delay line 7 an interactionspace :15 which is highly critical in the performance of backward wavetubes. With the delay line and body member at ground potential and thesole electrode-at a higher negative potential with respect to thecathode of the electron gun, an elect-ric eld is established in theinteraction space. By adjusting the sole electrode spacing While thetube is operating it will be possibleto optimize performance. The solepositioning mechanism comprises a rigid spider member 16 secured atspaced intervals to the sole electrode by means of screws 17, 18,19 and20. A non-magnetic metal, such as stain'- less steel is desirablyemployed for the spider member, as well as the screw members.` Thecentral portion 21 of spider member 16 is secured to a ribbed sleeve 22of an insulatingV material such as a ceramic having a highy aluminacontent. The sleeve 22 breaks the direct current contact between thesole electrode and the external ad; justing mechanism for positioningthis electrode.

The central portion of the ceramic sleeve is in turn secured to ametallic adjusting rod 23 having one end hollowed as at 24 and the otherend drilled and tapped as at 25. A deformable assembly is secured to theadjusting rod 23 comprising a two piece bellows diaphragm in which theinner member 26 is brazed to a shoulder on the rod and the outer member27 is brazed to metallic cover plate 3 by means of cup 28. The twomembers of the deformable assembly are brazed together by a radiofrequency induction technique to provide a vacuum joint and the metalemployed is desirably Monel.

The adjusting mechanism is positioned external to the tube envelope andis supported by a collar or housing member 29. An adjusting screw 32having a left-hand thread 33 and right-hand thread 34 is threaded intothe end 25 of rod 23. The opposite end of screw 32 extends throughhousing member 29 and threadably engages a push-pull plate 50 Amountedon top of the housing member. Both the plate S and housing member 29 aresecured to cover plate ,cup 28 by means of locking screws 30 and 31. Setnut 5-1 threaded at the endof rod 23 provides a secure bearing againstthe push-.pull plate l50. A recess 35 in the head of screw 32 providesmeans for introduction of an appropriate tool'to thereby produce axialmovement of screw 32 which is translated into movement of the soleelectrode along the plane of the magnetic eld of the device.

Within housing member 29, we next provide passageways spaced 90 apartwith threaded centering pins'36 therein. Ball bearings 37 are also.provided the housing member to contact the tapered portion of each pin36. A split Aring 38 attached to rod 23 also provides contact with theball hearings 37. Movement of pins 36 in and out of the .housingpassageways will then result in radical displacement ofthe soleelectrode.

Cylindrical magnetic pole piece 39 Vsurrounds the ,housing member 29 andis secured to cover plate 3. Thermagnet contacts the pole piece to formapart of-the overall tube magnetic circuit.

The cathode electrode or electron gun assembly `cornmonly found inbackward wave .oscillator tubes is positioned within a segment of thesole electrode and leads 40 extend through an insulated connection plate41 to the cathode and sole input vassembly 4Z. A hollow conductive pipe43 is connected to the sole electrode at one end and a ceramic insulator44 `at `the other end. A conical cup 45 `is brazed to insulator 44 andwelded by another flanged cup 46 secured to cover plate 4 to therebyprovide a vacuum tight envelope.

The output coupling assembly 47 isintroducedinto the envelope andcommunicates -wth the delay line ngers in the manner well-known in thealt. The overall tube assembly is evacuated after all brazing andwelding operations are completed by a suitable tubulation (not shown)which may be inserted through one of the cover plates.

After the tube has been completed, the appropriate electrical leads areconnected and the electrical performance may be evaluated. A simpleadjustment of the four radially disposed studs 36 or the screw 32 willthen provide for radial as Well as axial adjustment of the soleelectrode to optimize the electrical performance. Results of tubesincorporating the novel electrode positioning mechanism have shown `a to100% increase in power output over a selected frequency bandpassoompared with tubes not incorporating this structure. Elimination ofpower dips or holes as they are sometimes referred to, `have beenexperienced ina substantial number of tubes. Vibration and shockrequirements have also been lmet.

By way of illustration the following results have been tabulated showingelectricaldata of a Carcinotron tube operated before and afteradjustment of the sole electrode. v

1 Power below minimum.

While a specific illustrative embodiment has been described, manyalterations or modifications will be evident to skilled artisans. lt isour intention to cover such alterations or modifications as fall withinthe spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. In an electron discharge device of the circular backward wave typecomprising a cylindrical body member having end closure members disposednormal to the axis of the cylinder to define an envelope, concentricallydisposed conductors enclosed within said envelope including a circularmultifingered interdigital delay line supported by said body member andan inner negatively biased electrode spaced from said delay line todefine an interaction space, said inner electrode being externallyadjustable by mechanical means supported by an end closure member, saidmechanical means comprising a metallic member of non-magnetic metalsecured to a planar surface of said inner electrode, a non-conductivemember secured to said metallic member, a rod secured -to said metallicmember and extending axially through an end closure member, a deformablebellows structure joining said rod and end closure member to provide avacuum tight seal, an adjusting mechanism secured to the top wall ofsaid end closure member and communicating with the external end of saidrod, said adjusting means cornprising a plurality of radially disposedball bearing members and means for moving said bearing members normal-to the envelope axis to thereby contact said rod and displace saidinner electrode radially and screw means threadably engaging theexternal end of said rod to axially displace Vsaid inner electrode tothereby alter the concentric alignment between said circular delay lineand said inner electrode and optimize the electrical characteristics ofthe device.

2. An electron discharge device according to claim l wherein said screwmeans are provided with a left hand and a right hand screw thread.

3. An electron discharge device according to claim i wherein saidnon-magnetic metallic member is secured to -said electrode at aplurality of spaced points.

4. An electron discharge device according to claim l wherein saiddeformable bellows structure comprises a pair of inverted cup membersjoined together along a common wall.

5. An electron discharge device according to claim l wherein said meansfor moving said ball bearing members comprise threaded pins each havinga tapered portion in contact with a ball bearing member.

References Cited in the tile of this patent UNITED STATES PATENTS2,468,152 Woodyard Apr. 26, 1949 2,506,955 Fracassi May 9, 19502,786,959 Warneclie et al Mar. 26, 1957 2,878,412 Lally Mar. 17, 19592,888,597 Dohler et al. May 26, 1959

